- term =. 
curve of that angle by which the joints of all the brick-work 
are prefe i i 
its blade ; and 
and confequently fuch a want of folidity, as to appear inca- 
- ch 
y are allowed to be the weakeft parts 
arch; therefore it follows, as a natural conclufion, 
that the ftronger thefe parts are made, the better the whole 
arch will be able to counteraét the tendency of a fracture, 
and confequently the greater burthen it will be capable of 
fupporting, without the danger of givi way. 2 
Thus having, L prefume, fufficiently explained my objec- 
tions to the old groined arches, I will now fubmit a concife 
defcription of my new method of building them, referring 
my readers to the confideration of the model made for that 
purpofe, which, though confifting of a fingle arch only, will 
neverthelefs impart a competent idea of a continuation o 
umitances may make it neceflary. 
s, as thofe which are {quare. 
The four-inch receffes between the bafes of the ribs may, 
if thought belt, be filled up to the height of the {pringing 
be perfe& oGagons (as 
) 3 and confequently all 
would be lefs expofed 
¥ sre even by this method; but the fuper- 
ficial fpace of two feet fix inches in each pier would be 
The e&tangular piers, 
feet of the ribs, are four 
this {uperior and apparent 
will be a faving of room ami 
exclufive of t 
ed, which ari 
each other roader footing on the main body of 
the pier, independently of the intervening {pandrils, which- 
are to be carried up to the level of the extrados of the 
oangular piers from each other 1 
have fuppofed to be twenty-one feet, which alfo tallies with 
it is clear to every underftanding, that the new method, as 
ractifed with equal eafe to any di- 
menfions, and with any ind of arch. . 
I have intended the diagonal ribs to confift of two bricks 
a half on the face, and two bricks in thicknefs ;_ whi 
alfo may be made larger or 
the arch, the fize of the 
put upon them, e filling to 
and a half brick in thicknefs, as is ufual, which may alfo be 
made thicker whenever it i 
the fize of the ribs and piers. 
ing the model, that thefe ribs, 
ner or edge of a {quare pier, but from the fides of a folid 
except fuch cuttings as may 
be neceflary for bond alone ; and the wh i 
d together i 
mortar, would, according to the fabjoined mathe. 
calculation, be capable of fupporting upwards of 
twice and a half the weight which the common groined arch 
of equal magnitude could fuftain. iad : 
As the diagonal of a fquare is longer than one of its fides, 
i y obvious that the girth of the elliptic crofse 
bs mutt be greater than the girth of the femi-circular 
ttir ay and diminifhing the real by a 
itance of the bricks, and hereby falling inte one 
by thunning another. But as it frequea 
that which at the firft a me 
